Compared to other types of RF communication systems, automatic meter reading (“AMR”) systems are characterized by a relatively large number of meters that each transmit a relatively small amount of data infrequently at very low power. For example, a typical AMR system may include a number of data collection devices that each receive data from 10,000 to 100,000 meters reporting less than a kilobyte of data hourly at one mWatt. In the United States, the frequency band from 903 MHZ to 926 MHZ is available for this type of application but the governing regulations require very low broadcast power in the mWatt range. Other license exempt frequency bands around 2.4 GHZ and 5.8 GHZ are also available in the United States for some AMR applications, and a few different frequency bands are applicable in other countries. Within the license exempt frequency bands, the AMR communication protocol typically divides the operational frequency band into a number of channels and implements frequency or digital code hopping to reduce interference among the large number of transmitters using the frequency band. This enables the meters to transmit at one Watt rather than the one mWatt regulatory limit that applies to an unspread channel.
In general, AMR systems can be configured into coverage patterns based on the data handling capacities of the data collection devices and the transmission range and data transmission capacity of the meters. These components can be organized into simple point to multipoint configurations and more complex mesh networks. Ultimately, the cost and inefficiency of the AMR system can generally be reduced by increasing the data handling capacities of the data collection devices, the transmission range of the meters, and the data transmission capacities of the meters.
Conventional AMR systems are bandwidth limited, however, by the number of channels implemented by the communication protocol, the width of the channels, and the available gain in view of the broadcast power restrictions. Specifically, frequency or digital code hopping among the channels permits narrow band communication protocol within the spread spectrum, but does not offer any inherent performance advantage over single channel in terms of channel bandwidth. Conventional approaches to frequency or digital code hopping also limits the ability to further divide the operational frequency to achieve very narrow band performance. The frequency width of the narrow band communication channels limits the gain available within each channel. This can be a significant limitation at the low (e.g., mWatt) and medium (e.g., one Watt) power levels typical of AMR systems, often limiting the data transmission range to a kilometer or less. Frequency or digital code hopping to limit interference also prevents conventional AMR systems from implementing the types of multiplexing techniques used in mobile telephone and other RF applications to optimize the communication bandwidth. As a result, there is a continuing need for more efficient and effective communication protocols for AMR meter reading techniques, especially with regard to the issues of link budget and data rate, which have become increasingly pressing issues in recent years.